As widespread power outages cause chaos in Spain and Portugal, authorities are scrambling to determine what caused one of Europe’s biggest blackout.
Described as ‘catastrophically bad’, the outage grounded flights, sent roads into gridlock as traffic lights failed, and left entire cities without power or telecommunications.
Now, scientists reveal the true reason for the massive outage – and why the chaos is so widespread.
Experts say the blackout is likely due to a combination of factors including Spain’s reliance on green energy and ‘anomalous oscillations’ in power lines.
While authorities say that a cyberattack is not likely, the possibility of malicious interference has not yet been ruled out.
According to the Portuguese electricity operator Redes Energéticas Nacionais (REN), the blackouts began at 11:33 am BST on Monday.
Almost all of Spain and Portugal were affected as the Iberian Peninsula’s power grid was cut off from the wider European grid (ENTSO-E).
As of Tuesday morning, Spain’s biggest electricity operator, REE, says 92 per cent of Spain has had power restored while 80 per cent of customers in Portugal have electricity.
The power outage caused massive disruption as trains were cancelled and planes were grounded. Pictured: People wait outside Humberto Delago airport in Lisbon, Spain
‘RARE ATMOSPHERIC PHENOMENON’
On Monday, REN, Portugal’s grid operator, said the widespread blackouts over Spain and Portugal had been caused by a ‘rare atmospheric phenomenon’.
Extreme temperature variations along the grid caused ‘anomalous oscillations’ in high-voltage power lines, beginning in Spain and spreading into Portugal.
In a statement, REN said: ‘Due to extreme temperature variations in the interior of Spain, there were anomalous oscillations in the very high voltage lines.’
However, even the experts say it isn’t entirely clear what this might actually mean, and REN hasn’t given any extra details.
Professor Victor Becerra, Professor of Power Systems Engineering at the University of Portsmouth suggests that it could be related to the extreme wind created by temperature variations.
Professor Becerra says these high winds could have caused the cables to shake in an effect known as ‘galloping’.
This could have led to ‘potential mechanical failure, such as snapped conductors, short circuits, or damage to key infrastructure like transmission towers.’
On Monday, REN, Portugal’s grid operator, said the widespread blackouts over Spain and Portugal had been caused by a ‘rare atmospheric phenomenon’
Yesterday, Spain and Portugal were hit by cascading power outages which caused widespread blackouts. Pictured: People shop for groceries during a shutdown of electricity
Others have argued that, in extremely high temperatures, power cables can interact with induced electrical charges in the atmosphere – triggering vibrations.
Professor Chenghong Gu, an electrical engineering expert at the University of Bath, said: ‘This vibration can cause fatigue of conductors and in very extreme cases, failures of conductors.’
However, most of the scientific literature on the effects of temperature variations suggests that problems are likely to be caused by an imbalanced drain on the grid.
When one area is significantly hotter than another, its power demand is much greater as people use air conditioning to cool their homes.
This causes the voltage and frequency of some parts of the grid to get out of sync with the rest of the grid.
The differences between the different sections can lead to irregular or excessive power flow to some areas, damaging equipment and triggering widespread power failures.
In reality, the source of the cascading failure might have been a combination of different factors.
Heat variations may have caused winds or other disturbances which sent vibrations through the power grid. Pictured: Employees stand inside a supermarket without lights in Burgos on April 28, 2025
Professor David Brayshaw, Professor of Climate Science and Energy Meteorology at the University of Reading, says: ‘[Power systems] must balance supply and demand almost instantaneously, and generators need to stay precisely in sync.
‘If something on the network – a generator, a power line, or even a large electricity user – suddenly disappears, it creates a supply-demand imbalance, and the system frequency starts to shift.
‘If that shift becomes too large, other components can trip offline, creating a snowball effect that worsens the imbalance and can trigger a major blackout – sometimes within seconds.’
RELIANCE ON SOLAR AND WIND
The bigger question is why a localised fault was able to trigger such widespread disruption and cause one of Europe’s largest-ever blackouts.
Some have suggested that an extreme reliance on renewable energy sources including solar and wind may be responsible for the scale of the chaos.
Spain is uniquely dependent on renewable sources of power and has transitioned to a green network with exceptional speed.
Just two decades ago, 80 per cent of the country’s power came from fossil fuels such as coal and gas while renewables made up just five per cent.
Spain’s green energy revolution was under scrutiny yesterday for making massive power cuts ‘much worse’ as millions were plunged into blackout chaos. Pictured: Crowds waiting for a taxi at Barajas Airport in Madrid
But pandemonium struck at lunchtime yesterday when solar power and wind were together making up more than 80 per cent of electricity generation.
Traditional forms of power generation, including green options like nuclear or hydroelectric power, use spinning parts which build up ‘inertia’ as they move.
When there are changes to demand on the grid, these spinning parts can speed up or slow down to help keep the power frequency consistent.
This essentially acts like suspension for the power grid, helping it to absorb shocks from changes like sudden temperature variations.
Since solar panels and wind turbines don’t generate inertia, a grid heavy in these sources is more vulnerable to rapid changes.
Because Spain has very little power storage and lots of renewables, some experts believe a cascading issue was more likely to occur.
Kathryn Porter, an independent energy analyst, told The Telegraph: ‘In a low-inertia environment the frequency can change much faster.
‘If you have had a significant grid fault in one area, or a cyber-attack, or whatever it may be, the grid operators therefore have less time to react.’
Since Spain has lots of renewables and very little power storage, it is more vulnerable to cascading power failures. Pictured: A person walks down a downtown street during a power outage in Malaga on Tuesday
CYBER ATTACK
As the chaos spread, suspicion immediately turned to a cyberattack as a possible source of the disruption, while cannot be ruled out.
Steve Sandford, partner at cybersecurity firm CyXcel, told MailOnline: ‘While the exact cause of the outage is still under investigation, there are several factors that suggest that the blackouts could be caused by a cyber-related incident.
‘The sudden and dramatic drop in electricity demand, the widespread impact on critical infrastructure, and the disruption extending to parts of southern France and Andorra suggest a coordinated cyber-related incident.’
Mr Sandford adds: ‘Airports, metro systems, telecommunications networks, and traffic lights were all affected, which aligns with typical critical infrastructure targets.’
Although attacks on national infrastructure are rare, this would not be the first time that a nation’s electricity grid has been disrupted by a digital attack.
Jake Moore, global cybersecurity advisor at ESET, told MailOnline: ‘Power grids are tightly secured but all systems naturally have their vulnerabilities.
‘Outdated, legacy computers still feature in our critical national infrastructure and even in our banks which can often become an interesting target.’
Some have suggested that a cyberattack could be behind the blackout. Pictured: People wait for the metro to arrive at a station in Madrid, as metro operations resume partially
However, most experts say there is no evidence to suggest that a deliberate cyberattack was the cause of the disruption
In 2015, computers in the Ukrainian energy grid became infected by a malware called BlackEnergy which had been specifically designed to target industrial systems.
Once inside the network, the virus allowed hackers to remotely operate circuit breakers and erase key files on the target systems, rendering them inoperable.
While BlackEnergy is still causing issues for many in Western Ukraine, the initial attacks left approximately 225,000 people without power.
However, if cybercriminals truly were behind the attack, Spain and Portugal’s blackouts would be on a far grander scale.
Currently, experts and national authorities say there is no evidence that a cyberattack has taken place, but malicious interference is not being ruled out.
Adam Pilton, cybersecurity advisor at Heimdal Security and former cybercrime Detective Sergeant with Dorset Police, told MailOnline: ‘The department of national security has said that it is still too early to know what caused the power outage and nothing is ruled out.
‘It was only last month that we heard that a Chinese threat actor Volt Typhoon had hacked into a small public power utility in Massachusetts and then rather worryingly, the attackers sat there unnoticed for 300 days effectively spying on the power suppliers’ daily operations.’
Yet most experts, including Mr Pilton, currently believe that a cyberattack is not likely.
Transport infrastructure like traffic lights are a likely target for a nation-state cyber attack. Pictured: Traffic systems without power in Madrid on April 28
The European Council president, António Costa, who was Portugal’s prime minister from 2015 to 2024, said ‘there is no evidence that it was a cyber-attack’.
Likewise, European Commission vice-president Teresa Ribera told Spain’s Radio 5 that there was no evidence of criminals having caused the outage.
James Bore, managing director of cyber technology firm Bores Group, told MailOnline: ‘I can state, with 90 per cent certainty that it wasn’t a cyberattack.’
Mr Bore explains that the attack was ‘too poorly timed’ and included ‘no real sign of any way to profit’ – which makes a criminal attack unlikely.
Likewise, an attack on this scale would almost certainly require the resources and expertise of a nation-state or at least a nation-state-backed threat group – which is also extremely unlikely.
Mr Bore says: ‘The only places we’ve seen nation-state cyberattacks are as a support tactic for kinetic warfare, such as in Ukraine.
‘With the capabilities nation-states have and the potential damage that could be done in retaliation, there’s a reluctance to push conflicts into the cyber sphere where it comes to critical national infrastructure.’
